Electric circuit breaker with thermal magnetic trip



1966 R. T. CASEY ETAL 3,278,708

ELECTRIC CIRCUIT BREAKER WITH THERMAL MAGNETIC TRIP Filed Nov. 26, 1965 INVENTORS ROBE/F7 C455), K's/TH [4/ KLE/A/ TTQRNEV United States Patent 3 27s 708 ELECTRIC CIRCUIT IIREhKER WITH THERMAL MAGNETIC TRIP Robert T. Casey, Southington, and Keith W. Klein, Simsbury, C0nn., assignors to General Electric Company, a corporation of New York Filed Nov. 26, 1965, Ser. No. 509,938 3 Claims. (Cl. 200116) released causes automatic opening of the circuit breaker,

and which further includes thermal means and separate magnetic means for causing release of the releasable member.

In accordance with the prior art, electric circuit breakers of the small molded case type, such, for example, as shown in Patents 2,776,349 and 2,627,564, assigned to the same assignee as the present invention, include thermal and magnetic current responsive means for causing automatic opening of the circuit breaker upon the occurrence of predetermined current conditions. Such thermal and magnetic current responsive means commonly act on a latch member which holds a releasable trip member of the contact operating mechanism. The thermal current responsive device ordinarily comprises an elongated bimetallic strip which is supported upon a combined rigid terminal strap and support member. A power feed-in conductor is connected to the outer end of the terminal strap. During the process of connecting the feed-in conductor to the terminal strap, relatively high forces are often exerted on the outer end of the terminal strap, sometimes causing distortion of the strap and changes in the position of the bimetallic strip which is carried by the inner end of the terminal strap. This in turn causes changes in the adjustment or calibration of the circuit breaker, which is very undesirable.

In addition, it is desirable that the sensitivity of the magnetic current responsive device be higher than that which can be conveniently achieved with the constructions as shown in the aforesaid prior art patents. Accordingly, improved structures have been provided including a plurality of turns on the magnetic field piece to provide such increased sensitivity. A structure of the latter type referred to is shown in application Serial No. 405,699 filed October 22, 1964. The provision of such additional turns on the magnetic field piece, however, presents the problem of accommodating such turns in the limited space available.

It is an object of the present invention to provide an electric circuit breaker of the type described including thermal and magnetic trip means in which the mounting of the bimetallic strip is mechanically isolated, i.e., as regards mechanical forces, from the external terminal connecting means.

It is a further object of the invention to provide a thermal magnetic trip which also readily accommodates a multiturn magnetic trip device.

In accordance with the invention in one form, we provide an electric circuit breaker of the type having a manual and automatically operable mechanism including a member releasable to cause automatic opening of the circuit breaker. A primary latch member is provided which normally restrains movement of the releasable member. An elongated bimetallic strip or bimetal is provided, having one end supported on and electrically connected to a metallic conductive support member which is fixedly attached to the insulating casing. A multiturn magnetic winding interconnects the bimetal support member and an externally located terminal support member, A magnetic field piece is encircled by the winding and positioned to attract an armature pivotally mounted in the case. The armature in turn includes a portion having a connection with the primary latch member, whereby attraction of the armature to the magnet moves the primary lat-ch member in releasing direction. The bimetallic strip member is also connected directly to the latch member. Since the winding, which is resilient, is interposed between the terminal support member and the bimetallic strip support member, substantially no distorting forces are transmitted from the terminal support member to the bimetallic strip support member.

The invention will be more fully understood from the following detailed description, and its scope will be pointed out in the appended claims.

In the drawings,

FIGURE 1 is a side elevation view of an electric circuit breaker incorporating the invention, the side of the insulating casing nearest the observer being removed to show the internal parts;

FIGURE 2 is a fragmentary elevation view on larger scale of the trip mechanism portion of the circuit breaker of FIGURE 1, the bimetallic strip member being shown in thermally deflected condition due to electrical overload;

FIGURE 3 is a fragmentary view similar to FIGURE 2, showing the parts in a magnetically actuated condition, and

FIGURE 4 is a fragmentary perspective view of a portion of the mechanism of the circuit breaker of FIG- URE 1.

In the drawing, the invention is shown in FIGURE 1 as incorporated in an electric circuit breaker having a molded insulating casing 10 including a plurality of recesses and integral barriers for supporting and guiding the parts. The casing 10 is normally closed by a cover member, not shown, attached thereto by suitable means such as rivets, extending through openings 11 in the casing 10.

The stationary contact 12 is supported on a plug-in-type terminal member 13 which is trapped in conforming recesses in the casing 10. A movable contact 14 is mounted on the end of a contact arm 15, which is generally Y- shaped, having a pair of spaced leg portions 15A (only one shown) which are pivotally connected at 15B to an insulating operating handle 16. The handle 16 is pivotally mounted in the casing on an integral hub or axle 17. The contact arm 15 is connected by tension spring 18 to an intermediate point 19 of a releasable member or cradle 20 which is pivotally supported in the insulating casing 10 by pivot pin 21 and normally maintained in the position shown in FIGURE 1 by a latch member 40. The cradle member 20 also carries a reset pin 22 for a purpose to be described.

Operation of the handle 16 about its pivotal support 17 moves the supported portion 15B of the contact arm 15 back and forth across the line of action of the spring 18, thereby causing the contact arm 15 to snap between closed and open-circuit positions.

When the contact arm is in closed-circuit position, release of the cradle member from the latch 40 permits the cradle 20 to rotate clockwise about its pivotal support 21 under the bias of spring 18. This carries the line of action of the spring 18 across the pivot of the contact arm 15 and thereby reverses the bias of the spring 18 on the member 15, causing the contact arm 15 to automatically move to open-circuit position. Following such automatic opening or tripping, the cradle 20 may be reset to latched position by rotating the handle 16 clockwise engaging the pin 22 of the cradle and rotating it counter-clockwise to relatched position.

The movable contact 14 is connected by means of a flexible conductor 24 to an intermediate point 25 of a generally J-shaped elongated bimetallic strip 26 having a major straight portion 27 and a minor return-bent portion '28. The bimetallic strip 26 is fixedly mounted at the outer end of the straight portion 27 at point 29 on a bimetallic strip support member 30.

The support member 36 is fixedly mounted in the casing by means of an anchoring screw 311 which extends 4 is not deflected, nor is it bent or distorted by the force of the armature causing tripping.

Although the conductor 34 electrically interconnects the terminal support member 35 and the bimetallic strip support member '30, it does not transmit thereto mechanical forces which may be exerted on the terminal support member 35, such as in the proceses of connecting a conductor thereto. This is because the coil portion 34A acts to give this member a high degree of resilience.

It will be observed that movement of the latch member 40 by the bimetallic strip '26 as shown in FIGURE 2 does not change the position of the armature member 37, and therefore, does not alter the magnetic air gap. This means that the magnetic air gap setting is not changed by deflection of the bimetallic strip member which may change the position of the latch member 40 slightly before tripping occurs.

It will also be observed that the magnetic tripping by means of the armature '37 is not impeded by the bimetallic strip, since the armature member 37 can move the latch member 40 without restraint by the bimetallic strip memthrough a clearance hole in the casing '10 and into threaded engagement with the support member '30, drawing the support member 30 tightly against a pair of spaced projections 32, 32' in the casing. Tightening of the screw 31 causes the intermediate part of the support member 30 to bend, thereby changing the angle of the supporting portion which supports the bimetallic strip 26, thereby changing the adjustment or calibration of the circuit breaker.

The support member 30 is connected by an elongated conductor 34 to an external terminal support member 35 trapped in conforming recesses in the casing 10 and cover. The conductor 34 includes an intermediate winding portion 35 which surrounds a magnetic field piece 36 also rigidly trapped by conforming recesses in the casing and cover.

An elongated magnetic armature 37 is pivotally supported in the casing at 38, and has a bent-over end portion including a laterally off-set extension 39 which overlies the front surface of the main latch member 40 and a second laterally offset extension 39A. The magnetic armature 37 is biased clockwise to the position shown in FIGURE 1 in which the extension 39A abuts against a stop, not shown, in the casing 10. The armature 37 is biased in the manner described by means of a thin flat leaf spring 37A rigidly attached thereto and having its upper end resting against a boss 37B in the casing 10. The latch member 40 is pivotally mounted in the case at 41 and is biased in clockwise direction by compression spring 42. The return-bent portion 28 of the bimetallic strip 26 overlies the end portion 40 of the latch member 40.

As shown in FIGURE 1, the bent-over end portion 40' of the latch member 40 normally engages and restrains the cradle member 20 in the position shown in FIGURE 1. Referring to FIGURE 2, the parts are shown in the condition which they occupy immediately following thermal tripping. Thus upon the occurrence of .a moderate overload condition, the current passing through the bimetallic strip 26 heats this member, causing it to deflect as shown in FIGURE '2, the return-bent portion 28 moving the lower end of the latch member 40 to the right as viewed, releasing the cradle member 20, which thereupon moves to the tripped condition as previously described.

In FIGURE 3, the parts are shown in the condition which they occupy upon magnetic tripping. Thus, on the occurrence of a high overload or short circuit condition, the current through the winding 34A causes the magnetic field piece '36 to attract the armature 37, which pivots counterclockwise about its pivot 38. Movement of the armature 37 to the right as viewed in FIGURE 3 causes the iatch member 40 also to move in this direction because of the interconnection at point 39, causing the latch member 40 to release the cradle member 20. It will be observed that in this case, the bimetallic strip member 26 ber.

Although the invention has been shown in one specific embodiment, it will be readily apparent that many modifications thereof may be made by those skilled in the I art and it is therefore intended that the appended claims shall cover all such modifications as fall within the true spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. An electric circuit breaker comprising:

(a) an insulating casing;

(b) at least one pair of relatively separable contacts supported in said casing;

(c) operating mechanism supported in said casing and connected to at least one of said relatively movable contacts for moving said contacts between open and closed circuit conditions, said operating mechanism including a member releasable to cause movement of said contacts from said closed to said open circuit position;

(d) a latch member normally engaging and restraining said releasable member;

(e) .an elongated bimetallic strip;

(f) means rigidly anchoring one end of said bimetallic strip in said casing;

(g) means connecting the other end of said bimetallic strip to said latch member;

(h) a magnetic field member mounted in said insulating casing;

(i) an armature member movably supported parallel to said latch member in said insulating casing adjacent said field member;

(j) means separably connecting said armature member in spaced relation to said latch member;

(k) a terminal support member rigidly mounted on said insulating casing;

(1) an elongated electrical conductor connecting said terminal support member to said bimetallic strip adjacent said one end thereof;

(m) said conductor having an intermediate portion thereof encircling said field piece, whereby said intermediate portion acts as an energizing winding for said field piece upon the passage of current there through and also acts to minimize the transmission of force from said terminal support member to said bimetallic strip.

2. An electric circuit breaker as set forth in claim 1,

wherein said magnetic field member comprises a generally U-shaped piece, said bimetallic strip including a portion passing through said field member and between said field member and said armature member.

3. An electric circuit breaker as set forth in claim 1, wherein said means rigidly anchoring said one end of said bimetallic strip comprises a metallic supporting member rigidly attached to said insulating casing and wherein to said support member.

2,662,951 12/1953 Boiler et a1 20088 X said elongated conductor has one end thereof connected 3,178,535 4/ 1965 Gelzheiser et a1 20088 3,179,767 4/1965 Middenford 20088 References Cited by the Examiner 5 References Cited by the Applicant UNITED STATES PATENTS UNITED STATES PATENTS Hanny Th m s- 6/1931 Jennings 20088 8/1943 swingle 200 88 BERNARD A. GILHEANY, Pllmary Exammel. 9/1943 Jennings 20088 10 H. B. GILSON, Assistant Examiner. 10/ 1947 Jennings 20088 

1. AN ELECTRIC CIRCUIT BREAKER COMPRISING: (A) AN INSULATING CASING; (B) AT LEAST ONE PAIR OF RELATIVELY SEPARABLE CONTACTS SUPPORTED IN SAID CASING; (C) OPERATING MECHANISM SUPPORTED IN SAID CASING AND CONNECTED TO AT LEAST ONE OF SAID RELATIVELY MOVABLE CONTACTS FOR MOVING SAID CONTACTS BETWEEN OPEN AND CLOSED CIRCUIT CONDITIONS, SAID OPERATING MECHANISM INCLUDING A MEMBER RELEASABLE TO CAUSE MOVEMENT OF SAID CONTACTS FROM SAID CLOSED TO SAID OPEN CIRCUIT POSITION; (D) A LATCH MEMBER NORMALLY ENGAGING AND RESTRAINING SAID RELEASABLE MEMBER; (E) AN ELONGATED BIMETALLIC STRIP; (F) MEANS RIGIDLY ANCHORING ONE END OF SAID BIMETALLIC STRIP IN SAID CASING; (G) MEANS CONNECTING THE OTHER END OF SAID BIMETALLIC STRIP TO SAID LATCH MEMBER; (H) A MAGNETIC FIELD MEMBER MOUNTED IN SAID INSULATING CASING; (I) AN ARMATURE MEMBER MOVABLY SUPPORTED PARALLEL TO SAID LATCH MEMBER IN SAID INSULATING CASING ADJACENT SAID FIELD MEMBER; (J) MEANS SEPARABLY CONNECTING SAID ARMATURE MEMBER IN SPACED RELATION TO SAID LATCH MEMBER; (K) A TERMINAL SUPPORT MEMBER RIGIDLY MOUNTED ON SAID INSULATING CASING; (L) AN ELONGATED ELECTRICAL CONDUCTOR CONNECTING SAID TERMINAL SUPPORT MEMBER TO SAID BIMETALLIC STRIP ADJACENT SAID ONE END THEREOF; (M) SAID CONDUCTOR HAVING AN INTERMEDIATE PORTION THEREOF ENCIRCLING SAID FIELD PIECE, WHEREBY SAID INTERMEDIATE PORTION ACTS AS AN ENERGIZING WINDING FOR SAID FIELD PIECE UPON THE PASSAGE OF CURRENT THERETHROUGH AND ALSO ACTS TO MINIMIZE THE TRANSMISSION OF FORCE FROM SAID TERMINAL SUPPORT MEMBER TO SAID BIMETALLIC STRIP. 